Process and apparatus for controlling the density of the apex discharge of a cyclone



Aug- 11, l953 o. H. WRIGHT ET AL 2,648,433

PRocEss AND APPARATUS EDR coNTRoLEING THE DENSITY 0E TRE APEX DISCHARGE DE A cYcLoNE Filed Dec. 5, 195o s sheets-sneet 1 EJO ATTORNEY ETAL 2,648,433 ROLLING THE DENSITY 0F A cYCLoNE Allgl1, 1953 o. H. WRIGHT PROCESS AND APPARATUS FOR CONT OF THE APEX DISCHARGE Filed Deo. 5, 1950 3 Sheets-Sheet 2 ATTORNEY Aug. l1, 1953 o PROCESS AND APPRAT oF THE APEX Filed Dec. 5, 195o H WRIGHT ET AL US FOR CONTROLLING THE DENSITY,

DISCHARGE OF A CYCLONE 5 Sheets-Sheet 3 auf, i

/" ATTORNEY INVENTORS process takes place.

Patented Aug. 11, 1953 PROCESS AND APPARATUS FOR CONTROL- LING THE DENSITY OF THE APEX DIS- CHARGE F A CYCLONE Orrin Hughitt Wright and Joseph Leonard Weaver, Brewster, Fla., Fitch, Westport, Conn. Weaver assignors, by Naamloze Vennootschap Maatschappij and Elliot Bryant said Wright and said mesne assignments, to

Kolenberwerking Stamicarbon, Heerlen, Netherlands, and said Fitch assigner to Ilhe Dorr Company, Delaware Stamford, Conn., a corporation of Application December 5, 1950, Serial No. 199,309

17 Claims.

This invention relates to cyclones. More specically this invention relates to a process of controlling the consistency of the discharge from the apex of a hydraulic cyclone and to apparatus for effecting this control automatically.

Cyclones have long been widely employed for the dewatering, desliming, and classification of uid slurries. They have also been used with finely divided media for the performance of separations based on specific gravity differences utilising centrifugal force to eifect the separation.

Generally, they are constructed in the form of a hollow cylinder or cone wherein the separatory For simplicity their operation will be described with particular reference to the conical type as each type of cyclone operates according to the same general principles, and the phrase apex orifice will be used hereinafter to describe the opening from which the heavy fraction is emitted not only from the conical type cyclone but from the cylindrical type cyclone as well.

The feed, a pumpable slurry, enters the cone tangentially through a feed inlet port near the base at a pressure which may be as low as lbs/in.2 or lower, and as high as 200 lbs/in.2 or higher, and spirals towards the apex of the cone in circles of decreasing diameter with inl creasing angular velocity. As a result, two concentric vortices form, creating a central air column. Both vortices rotate in the same direction but their liows are opposed, the inner vortex moving axially to the base of the cone and the outer vortex moving axially to the apex. The heavier constituent of the feed is thrown by centrifugal force into the outer vortex, and the lighter constituents, usually water and slimes in the case of desliming operations, and water and the lighter fraction of the feed in the case of specific gravity separations, are forced towards the inner vortex. The resultant of the forces within the cone causes these lighter constituents to travel along the inner vortex towards the base of the cone, exiting through a base orifice or passageway axially disposed therethrough, while the heavier constituents travel in the outer vortex towards the apex and are discharged through an orifice of denite size.

The operation of the cyclone is influenced by lmany factors-including feed pressure, area of Cil feed entrance, percent solids in feed, size distribution of solids in feed, 4size of base outlet, and size of apex orifice. Since it is practically impossible in ordinary operations to keep the feed variables constant or to change the basic cyclone structure, there is, as a result, a tendency with changes in feed for the characteristics of the two discharges from the cyclone to vary in their composition. Consequently, in attempting to control this, the most critical of the factors above mentioned which are capable of practical control is the size of the apex orifice.

When the cyclone is used as a thickener or classifier, it is of course desirable to produce as dense an apex discharge as possible. In a similar manner, some cyclone separatory processes have to operate with a maximum density of apex discharge in order to effect separation at a suiiiciently high gravity with lighter and cheaper solids such as magnetite.

Unfortunately when a cyclone operates under conditions closely approaching maximum `consistency of the apex discharge, small changes in any of the factors referred to above may increase t-he consistency to the point where the apex discharge becomes sausage-like or, as it is usually described ropy. When this condition prevails there is no longer a hollow central air column or core extending through the apex. Even when this condition sets in, the ropy type or discharge frequently extends up into the cyclone resulting in plugging. It has therefore been necessary in the past to operate cyclone thickeners with an apex discharge having a consistency sufliciently more fluid than that of a ropy discharge so that there is a suihcient margin of safety. Even the most critical manual supervision can not be relied on to prevent plugging if the cyclone is to be operated very close to maximum apex discharge consistency. Plugging soon results in serious contamination of the overflow product discharge, and when the plugging is complete, no thickening or classincation takes place, all the feed being discharged through the base of the cyclone. In the case of cyclones operating as separators, plugging changes the gravity at which separation takes place and results in contaminated products due to incomplete separation.

According to the present invention it has been found that the operation of a cyclone can be controlled manually and preferably automatically, near maximum apex discharge consistency without any danger of overloading or plugging. The invention is carried out by applying a partial vacuum to the central air column in the vortex finder of the cyclone. Preferably this is done by applying a suction to the central air column or core which persists in the middle of the vortex of the overfiow after it has been discharged from the cyclone.

It has been found that the vacuum in the central air column does not vary with the consistency of the apex discharge in a uniform manner. At very low apex discharge consistencies, when the consistency of the discharge is extremely fluid, the discharge is emitted as a spray and the increase n vacuum with increase in apex discharge consistency approaches linearity in this zone, the slope of the curve in this zone varying with different feeds and with different designs of cyclone. When the apex discharge begins to approach the consistency lof a cohesive discharge, the curve changes its character and becomes much steeper, the steepness in this second zone increasing as the consistency of the apex discharge becomes ropy. At a point where the discharge becomes sausage-like and there is no significant remaining central air column in the apex, the vacuum reaches a maximum. Thereafter, in this third zone there is no increase in vacuum with further decrease in apex diameter as the cyclone begins to plug up.

The sharp change in characteristics of the curve as the danger point is approached makes it possible by means of the present invention to effect reliable control at a maximum apex discharge consistency approaching maximum discharge density for the particular operation. The

steep part of the curve, that is to say the second zone where the rate of increase of vacuum with increase of discharge consistency is markedly greater than that of the lower portion of the curve, permits accurate control because there is a. relatively much greater change in vacuum with each change of density. As pointed out above, the exact shape of the curve varies with the nature of the feed and design of the cyclone. It is possible to use the present invention to control the apex discharge density on the steep Zone of the curve. There is, therefore, a choice of the particular density at which the apex discharge is to be maintained. Controlling it at the lower part of the steep zone of the curve where the discharge is usually of the spray type gives maximum safety but does not give as high an apex discharge density as is possible by controlling within a higher range of the curve where the discharge is usually of the cohesive, non-spraying type. The exact range depends on the relative economic factors involved and is further discussed below.

As a result of these discoveries, it has been found that when a pressure responsive means is made to communicate with the partial vacuum in the central air column and when said means is made to actuate a valve controlling the flow of discharge through the apex orice so that the valve is opened somewhat when the vacuum in the central air column increases above a predetermined value, and so that the valve is closed somewhat when the reverse takes place, and the vacuum is thereby maintained substantially constant, a discharge of substantially uniform consistency is obtained despite changes in the density of the feed and the danger of plugging is completely and automatically obviated. In brief, the flow of apex discharge is controlled so as to oppose changes in the partial vacuum.

As a further result, it has been found possible to operate a cyclone so that irrespective of other variations it uniformly yields an apex discharge which has a consistency which closely approximates the highest which can be discharged through the apex.

Hereinafter the degree of the vacuum referred to above may be referred to as pressure differentia that is, as the difference in pressure between atmospheric pressure and the pressure in the central air column, and the scale of inches of water will be uniformly used in connection therewith.

It is a further advantage that conventional cyclones can be readily altered to permit the practice of the present invention and that otherwise no particular form of apparatus is required When the instant invention is practiced automatically.

The invention will be further described with reference to the drawings in which:

Fig, 1 is a graph showing a plot of the air pressure differentials existing in the central air column of a cyclone during a typical run illustrating the present invention against the respective apex discharge densities obtained;

Fig. 2 is a vertical section of one form of apparatus according to the present invention; and

Fig. 3 is a vertical section of a second form of apparatus according to the present invention.

Fig. 1 is a plot of data accumulated during a typical run made in a cyclone modified according t0 the present invention, with manual control of the apex valve. This run was made in a twelveinch cyclone fed with a slurry of about 43.7% crushed limestone and Water having a specific gravity of about 1.4 which was pumped into the cyclone at a pressure of about 25 lbs/in.2 through a feed entrance about 5.72 in.2 in area. The cyclone was provided with a suction leg which was capable of producing a maximum vacuum equal to about inches of water. In this run the diameter of the apex discharge valve was at a maximum at the beginning of the run, and was continuously constricted manually to a minimum at which plugging of the cycle occurred. The specic gravity of the apex discharge and the corresponding pressure differentials in the central air column were noted at intervals during the run. At the beginning, the discharge was whirled out in so fluid a spray that the rush of air entering the apex could be detected by ear, the specific gravity of the apex discharge approximated that of the feed, the pressure differential in the central air column was low and in its rate of increase was essentially linear. In that zone, with gradual constriction of the apex valve both the specific gravity of the discharge and the pressure differential in the central air column slowly increased. When, however, the density of the apex discharge reached about 1.89 at a pressure differential of about 2 inches of water, formation of a slightly cohesive discharge began and departure from the essentially linear increase in the central air column pressure differential began. With further constriction of the valve the consistency of the discharge and rate of increase of the pressure differential increased more rapidly, while the density increased relatively slightly. Plugging occurred when the pressure differential was about 70 inches of Water corresponding to an apex discharge specific gravity of about 2.08. At that point the central air column was blocked at the apex, feed began to pass into the overflow conduit, and the curve abruptly leveled olf. Continuing to decrease the diameter of the apex valve caused no increase in vacuum above this maximum, although minor fluctuations occurred thereafter.

The points observed during this run were as follows:

Apex Discharge Vacuum, Inches H Speciiic Percent Gravity Solids there is nothing critical about any of the mag- I nitudes set forth in Fig. 1. The specic gravity of the slurry being treated may differ widely from that employed. The maximum pressure differential may be greater or less than that shown with a resulting accentuation of diminution of 3 the slope of the curve, and the point at which the curve begins to rise steeply may vary as the result of a combination of factors. In every instance, there will be found a Zone Where control according to the process of the present invention is feasible.

Fig. 2 is a section of one form of apparatus suitable for the practice of the instant invention, and will be described according to its mode of operation. A conventional cyclone I is shown having feed conduit 2 with tangential inlet port 3 in head casing 4 and a base outlet passageway or tubular exit from the base. In one form, this tubular exit may have a section 5 axially located within the cyclone and extending toward the apex beyond port 3, but it essentially comprises curved overflow discharge conduit 6, horizontal conduit 'I, curved conduit 8, `and vertical suction leg 9. Feed entering under pressure rotates within head casing 4 and is impelled into cone I where the speed of rotation increases as the feed proceeds in the direction of apex I0. As a result, two vortices are created `rotating in the same direction but having opposed axial ilow components. In normal operation, the central air column described above extends through the cone, beginning at the apex and continues through the base outlet passageway. The lighter components of the feed are forced inwardly, be-

come part of the inner vortex, travel upwardly, and leave the cyclone at orifice I I. The heavier components are thrown outwardly, become part of the outer vortex, and are discharged with a rotational movement which varies with their consistency through apex I0.

The discharge through orifice II `is a slurry containing entrained air rapidly rotating about its central air column. It passes into conduits B, 'I and 8, provided with air-tight couplings 26 wherein the central air -column is dissipated,

. 6 forming a liquid seal to the cone. The slurry.- now substantially freed of its rotational movement but containing the entrained air. passes through suction leg 9, which is suiciently long to produce the desired degree of vacuum in the central air column. Conduit 6 is perforated to admit hollow vacuum probe I2 through air-tight gland 25 which terminates within the base outlet passageway on cyclone axis 21 and which is connected to a conventional vacuum relay I5 through trap I3 and conduits I4 and 28. The vacuum relay is provided with compressed air supply I6, compressed air exhaust II, and supplies rubber pneumatic sphincter valve I8 in valve housing 29 with compressed air through line I9. As a result, the sphincter valve inates and partially closes when the pressure differential at orifice II is below a predetermined value, and partially opens when the pressure differential is above that predetermined value. The discharge from apex III passes first through apex conduit 20 and then through spray shield 2I.

The above type of apparatus permits come pletely automatic control of the consistency of the discharge. When manual operation is desired. valve 24 may be closed to cut off the relay, and the pressure differentials are read directly on the manometer 23 by opening valve 22. Manual control of the air supply to sphincter valve I8 is effected by operating the supply valve in relay I 5 which being conventional is not shown.

Fig. 3 is a different form of the apparatus of Fig. 2 utilizing, however, the same general principles. Feed enters through conduit 30 and passes tangentially through port 3l into upper casing 32 wherein it rotates and forms the two vortices in cone 33, described above. The upper vortex comprising the lighter constituents travels through base outlet section 34 into overflow chamber 35 where the central air column is dissipated by an abrupt change in its direction, the overflow leaving through pipe 36 which connects with a suction leg of the same design as that shown under Fig. 2, with similar entrainment of air. In ordinary operation the discharge through the base outlet section 34 does not completely ll chamber 35. A partial vacuum varying with the vacuum in base outlet section 34 therefore normally exists in the central portion of this chamber and is taken olf by vacuum probe 3l through vacuum probe line 31a. to conventional vacuum relay 52 of the mechanical type. Compressed air is supplied to this relay at inlet 33. Fluctuations in the vacuum in line 31a. control the air ram in ram housing 4I by unbalancing the balanced proportions of compressed air or oil which is supplied through lines 39 and 48 to opposed ends of the ram. Provision is made for limiting travel of the ram duringr this unbalancing by return motion lever 40 which rebalances the air or oil in lines 39 and 48 when the ram has travelled a predetermined distance. Maintenance of the desired vacuum in line 31a is effected by adjusting control knob 50 which controls the loading on the conventional measuring diaphragm of the apparatus. The air is exhausted from the relay in a pulsating stream at orillce 49 corresponding to pulsations in vacuum line 31u. The ram housing 4I is mounted on adjustable jack 42, so that it may be adjusted to the optimum operating position of apex orice plate valve 43. This valve is mounted on shaft 44 which passes through apex spray shield conduit 45 within gland 46 and opens and closes apex orifice 4'I, accomplishing substantially the same result in substantially the same manner as the sphincter valve of Fig. 2. The discharge from orifice 41 and spray shield 45 flows through transfer conduit I to waste or to storage as may be desired.

Any type of vacuum probe may be used so long as it will permit determination of the pressure differential in the central air column without undue disturbance of the vortex. As shown in the figures this may be an open ended pipe of relatively small diameter, but is not limited thereto, and includes vacuum probes of other types including the electric diaphragm type. Preferably it enters the cyclone centrally, that is, on an axis of the base orifice.

The position of the sensitive portion of the probe is of greater interest. It need not terminate in the same positions shown in Figs. 2 and 3. All that is necessary is that it terminate or have its vacuum sensitive part located at such a point that it will indicate the pressure differential in the central air column of the cyclone. In Fig. 3, the probe is shown as terminating in the air space formed in the center of chamber 35, as it has been found that the air pressure here varies Very closely with variations in the pressure in the central air column in the vortex finder. Accordingly, this position satisfies the requirement for most operations. Unusually turbulent ilow of liquid through the overflow chamber occasionally results inthe development of back pressure in the probe, and it has been discovered that the ideal location for the probe, suitable for virtually all types of operations, is within the vortex finder itself. Or-

dinarily it is not advantageous to extend the probe so that it passes completely through the vortex finder and into the body of the cone as the same back pressure noted above occasionally develops with the probe in this position. A preferred location is shown in Fig. 2 where the probe terminates about one-half a diameter of the vortex n-der below the outlet end of the vortex finder. In liquid cyclones without vortex nders the sensitive portion of the probe is preferably terminated on the axis of the base passageway within the central air core, and slightly above the opening of that passageway into the hydraulic cyclone, and in no event, of course,

should the pressure responsive portion of the I probe terminate in a current of slurry.

The vacuum relays are not critical in the instant invention. They are conventional and may be replaced by any device which will cause the apex valve to open and close somewhat with changes of vacuum in the central air column. In fact in small cyclones the vacuum relay may be omitted entirely and the apex valve, which may be of the iris type, may be actuated by a mechanical linkage operated by the vacuum probe. In larger installations, the relay becomes necessary.A

One preferred form of relay, specially suitable for operating the sphincter valve shown in Fig'. 2, is constructed by bringing the vacuum line to one end of an open-ended mercury manometer connected by pneumatic and mechanical linkages which operates a controlling and recording controller, such as a Foxboro Model 40 Stabilog Controller provided with manual control sub-panel and followed by a suitable air booster to give the required range of output pressure. This controller, when operating on an air supply of about 80 p. s. i. pressure, rapidly maintains the sphincter valve at such aperatures that the vortex 8. vacuum is maintained very constant with an almost unnoticeable degree of hunting. Another alternative controlling device is that shown in' Fig. 3. In devices of the latter type, any change in the air pressure on the measuring diaphragm is communicated to a delicately controlled multiplying valve. When the forces on the measuring diaphragm change, full air or oil pressure is thrown on the power piston moving it to a new position until the measuring diaphragm is once more in a state of equilibrium. One such device is the widely-known commercial Republic Pneumatic Type Regulator Series 65 which appears to have the advantage of reliability but which also appears to be incapable of producing.

as rapid control as the Foxboro pneumatic relay `system described above. The Republic nowmeter is described at pages 1-3 of Section E of Data Book NQS-13 copyrighted in 1938 by Republic Flow Meters Co.

While the automatic apparatus discussed above gives the best results and is therefore preferred, not all of this equipment is required to carry out the essentials of the instant invention. As stated,v

it is possible to practice the instant invention manually, and this may become necessary during an emergency. To permit manual operation, the apex valve is made manually operable, the relay system is shut off and. the vacuum probe is connected directly to an open ended manometer or equivalent vacuum gauge. The apex valve is then manually controlled to maintain the pressure differential in the central air column substantially constant at a predetermined value. With sufcient practice a surprisingly uniform discharge can be thus obtained, and it is a particular advantage that by use of the vacuum gauge it is not necessary for the operator to watch the apex product at all. Manual operation, while feasible, requires close supervision and ordinarily is not preferred as fully automatic operation gives more uniform results with elimination of one factor of expense.

The maximum degree of vacuum developed in the central air column by the suction leg or other vacuum producing device when the apex valve is closed is not critical as all that is necessary is that there be a measurable difference between the degree of partial vacuum existing when the cyclone is being operated normally and when the central air column is blocked or plugged. It is difficult to maintain an adequate degree of control when this difference amounts to only a few inches of water. Ordinarily, the maximum vacuum should be at least about six inches of Water as this gives a suiciently large measurable difference when the normal operating pressure differential is about 2.5 inches of water. Much better results are obtained when the maximum vacuum is increased to about 70 inches of water since the slope of the curve in this range is steeper. When discharges of a high degree of consistency are desired, a maximum degree of vacuum of about to 150 inches of water is usually found preferable because with these higher vacua, the curve rises much more abruptly, a large difference in the vacuum corresponding to only minor differences in the density of the apex discharge and much more precise control becomes possible. No limit can be set on the maximum degree of vacuum which should be provided for any one installation as this depends upon such variables as the specic gravity of the apex discharge, size of the particles in the feed, the boiling point of the liquid component of the slurry, and the temdesdits per'ature f the slurry. It is unnecessary of course te provide a 'greater degree of vacuum than is fund to yield the precision of control desired.

Combinations 'of the cirip'onehts shown in Figs. and 3 are also possible. For eitaiple, the Republic relaysho'wn' ih Fg. 3 be used to replace the Foxboro system shown in Fig. 2, and conversely, the Foxboro relay system described as suitable for the operation of the sphinete'r valve `in Fig. 2 may' be applied to the" entrolof the plat-e valve shown in Fig. In the latter` event the air ram shown in Fig. 3 may' be replaced if desired by an electric motor.

1 In accordance with good engineering practice, a liquid trap should protect the relay, and this lis particularly desirable where the vacuum probe' is'located in the head chamber as shown in Fig. 3. The vacuum line and the compressed air line leading to the apex valve shouldk be as sho'rt as possible `where a continuous, as distinct from intermittent, discharge from the apex is desired.

The apex valve may be of any suitable form which will permit the orifice of the cone to be constricted or enlarged suiiiciently wto provide sufhcient control of the central air column pres; sure differential. Ordinarily the valve need not have sufficient travel either to completely close the orifice or to open it completely. In actual practice it has generally been found sucient if the valveis capable of enlarging or decreasing the area of the orifice by 20% or 30% on either side of the average optimum aperture determined for the slurry employed.

The suction leg is another conventional piece of apparatus, the purpose of which is merely to evacuate air from the top of the central air column of the cyclone. It may be replaced by any other device which will perform a similar task such as a rotary pump or a steam ejector. When a suction leg is employed it may serve the added purpose of a transfer conduit and therefore need not be exactly vertical as shown. In fact, suflicient suction has been produced when the leg was extended into a horizontal plane, and even when slightly elevated.

The rate of discharge from the apex of the cyclone of the present invention is pulsating when a relay is used which hunts. When the sphincter valve-Foxboro relay combination of Fig. 2 is eme ployed, these pulsations are essentially damped out .by the anticipating mechanism of the relay and cannot be detected. With the slower air relay-plate valve combination of Fig. 3, some variations in the rate of discharge of product from the apex can be noted sometimes even when the orice is never completely shut. It is possible to increase these variations and a pulsating dise charge is' often desirable when very dilute slurries are processed, as it is sometimes diiiicult to obtai-n an apex discharge of maximum density with a relay which does not hunt. In processing dilute slurries' of this type particularly in very large industrial cyclones the apex of the cycloneA may sometimes be closed completely for a few seconds.

To calibrate the automatic regulators and to initiate automatic operation of the process, the automatic control is cut off andA provisiony is made for manual control of the apex valve. With the apexvalveY fully open, feed is admitted to the cyclone at normal operating rate andV pressure. The apexV valve is then manually closed until arr apex discharge of thev desired consistency isobl" tained. This discharge may be of the fiuid spray type or may be somewhat more cohesive. t4 the' desired point, the valve should" be' about in a Where the density y 10 half-opened petition. A1f it is at che extreme ci the other of closure, it sliul'd of 1ciirse berepiaced tithe valve ef istie suitable size. The pressure differential iiil the lcentral 'air 'commu then noted and the automatic regulator cu't in t maintain this differential dehstaiit thereafter.

During this procedure f adjustment the apexv anti the everfinw discharges may bei eeiiieiheu .the te returned te the ieee by subsi' airy circuits which are no part of the preseht invention. l

In the drawings the cyclone has been "shwn as Iriiint'ed vertically; Since the' 'separatory efli' ciehcy of the 'cyclne doesnot depend on gravity' eut resists from the application ef centiifuga-i forces, the bodyof the cyclone may be mounted in any plane. The' suction leg, however, should preferably extend in a generally downward dletii; 1 Y

In 'additidn to its 'Y use in den'sifyirig and thicken'- ig cyclones, ask described above, the procedure of the present invention is also of value in the control f cyclone separators; for example Vsuch as are described in Driessen et al. Dutch Patent No. 58,482 expiring October 16, 1964, particularly of the desired discharge lies on a sufficiently steep portion of the curve of the type 'of Fig. 1. The applicability of the instant procedure to these separatory cyclones where a medium is used, is influenced by such factors as the specic gravity, particle size and concentration of the medium solids as well as,- of course; by the character of the coal, ore,v or other matter in the medium. For example, when a ferrosilicon medium of low gravity and thin coni sistency is employed, the density of the apex discharge may be on the straight portion of the curve, but when magnetite is added to such a feed to give a medium of a greater consistency con"- taining a greater proportion of particles,- fully automatic control on the steep portion of the slope usually becomes possible.

In the drawings,- only conical cyclones have been shown, but it will be understood that the invention -may be practised in cyclones of the cylindrical type as well. Accordingly, in the claims, the word apex is used todesignate the p ortion' o f the cone orV cylinder through which the heaviergfraction Yof the feed is discharged.

Also, in the drawings and in the, foregoing specification, a,v conventional hydraulic cyclone vortex nders;

has been described with a conventional tubular exit from the ,basei Inthe drawings, such anr exit and element 5 in Fig. 1 and element 34 in Fig; 3, sometimes are referred to in the industry as but the description of the base oriiice passageway or tubular exit from the base that embodies the passageway, is not intended to restrict the invention to the use of vortex finders, since the invention is operable when embodied in a` hydraulic cyclone Without a vortex finder. Either with or without a vortex finder; the essentialparti'al vacuum will appear in the air core at a point near the base outlet und-er the disclosed conditions.

l; A method of controlling the cnsi'stenc'y' of tl'ie"v apex discharge of a; hydraulic cyclone, said cyclone having a tangential feed niiet port lo; cated near the base thereof, an' orificeex'ten'ding' through said base, arid orihc'e at the apex or said cyclone, which comprises introducing a sus-2^ pez'isi'on of solids through saif'd feed" port into said cyclone' at a pressure suinc rit to produce centrifugal forees greatly" in' excess of gravity, whereby tivo concentric vortices' rtatihg centen:

trically about a central air column and having opposed axial now components are formed in said cyclone, the outer vortex being discharged from the cyclone through the orifice in the apex thereof and the inner vortex being discharged from the cyclone through an orifice in the base thereof applying a substantially constant suction to the discharge from said base orifice thereby producing a partial vacuum in said central air column; varying the rate of ow of discharge through said apex orifice and thereby varying the density of said discharge over the range between a discharge of maximum and minimum fluidity whereby the partial vacuum in said central air column varies from a minimum to a maximum value, a graph of the variations in the partial vacua in said central air column versus the density of the corresponding discharges having at least three zones, a first zone where the vacuum in said central air column increases slowly and essentially linearly with the increase in the density of said discharge, a second zone where said vacuum increases relatively rapidly with further increase in the density of said discharge, and a third zone where the vacuum in said central air column approximates that of said applied vacuum; adjusting the rate of flow of said apex discharge until an apex discharge is obtained which has a density within said second zone, and thereafter increasing said rate of apex discharge when the partial vacuum in said central air column increases and decreasing said rate of discharge when said vacuum decreases and thereby maintaining the consistency of said apex discharge substantially constant.

2. A method of automtically controlling the consistency of the apex discharge of a hydraulic cyclone, said cylone having a tangential feed inlet port located near the base thereof, an orice extending through said base, and an orifice at the apex of said cylone, which comprises introducing a suspension of solids through said feed port into said cylone at a pressure sufficient to produce centrifugal forces greatly in excess of gravity, whereby two concentric vortices rotating concentrically about a central air column and having opposed axial flow components are formed in said cylone, the outer vortex being discharged from the cyclone through the orifice in the apex thereof and the inner vortex being discharged from the cyclone through the orifice in the base thereof; applying a substantially constant suction to the discharge from said base orifice thereby producing a partial vacuum in said central air column; varying the rate of ow of discharge through said apex orifice and thereby varying the density of said discharge over the range between a discharge of maximum and minimum fluidity whereby the partial vacuum in said central air column varies from a minimum to a maximum value, a graph of the variations in the partial vacua in said central air column versus the density of the corresponding discharges having at least three Zones, a first Zone where the vacuum in said central air column increases slowly and essentially linearly with the increase in the density of said discharge;' a second Vzone where said vacuum increases relatively rapidly j with further increase in the density of said discharge, and a third zone where the vacuum in said central air column approximates that of said applied vacuum; adjusting the rate of ilow of said apex discharge obtained which has a density within said' second zone, and thereafter increasing said rate of apex until 'an apex discharge is c discharge when the partial vacuum in said central air column increases and decreasing said rate of discharge when said vacuum decreases and thereby maintaining the consistency of said apex discharge substantially constant, said control being effected automatically by an apex discharge control actuated by changes in the partial vacuum in said base orifice in a direction to oppose changes in said partial vacuum.

3. A process according to claim 2 wherein the rate of flow of discharge through the apex orice is varied by altering the area of said apex orifice.

4. A process according to claim 3 wherein the substantially constant suction is applied to the discharge from the base orifice by dissipating the central air column in said discharge and then passing said discharge into a downwardly extending suction leg.

5. A method according to claim 4, in which the discharge is maintained at a consistency where the discharge is emitted as a spray and where a slight increase in the density of said discharge causes formation of a discharge of non-spraying consistency.

6. A method of automatically controlling the consistency of the apex discharge of a hydraulic cyclone, said cyclone having a tangential feed inlet port located near the base thereof, an orifice extending through said base, and a variable orifice at the apex of said cyclone, which comprises introducing a suspension of solids through said feed port into said cyclone at a pressure sufcient to produce centrifugal forces greatly in excess of gravity, whereby two concentric vortices rotating concentrically about a central air column and having opposed axial flow components are formed in said cyclone, the outer vortex being discharged from the cyclone through the orce in the apex thereof and the inner vortex being discharged from the cyclone through the orfice in the base thereof; passing the discharge from said base orifice into a suction leg thereby producing a partial vacuum in said central air column; varying the area of said apex orifice and thereby varying the density of said discharge over the range between a discharge of maximum and minimum fluidity whereby the partial vacuum in said central air column varies from a minimum to a maximum value, a graph of the variations in the partial vacua in said central air co1- umn versus the density of the corresponding discharges having at least three zones, a first zone where the vacuum in said central air column increases slowly and essentially linearly with increase in the density of said discharge, a second zone where said vacuum increases relatively rapidly with further increase in the density of said discharge, and a third zone where the vacuum in said central air column approximates that of said applied vacuum; adjusting the area of said apex orifice until an apex discharge of the cohesive type is obtained which has a density within said second zone, and thereafter increasing the area of said apex orifice when the partial vacuum in said central air column increases and decreasing the area of said apex orifice when said vacuum decreases and thereby maintaining the consistency of said apex discharge substantially constant, said control being effected automatically by an apex valve control actuated by changes in the partial vacuum in said base oririce in a direction to oppose changes in said partial vacuum.

7. A process according to claim 2 wherein the 13 flow of discharge from the apex is substantially constant.

8. The continuous process of classifying a mixture of ever-varying composition of solids in suspension into fractions, comprising establishing and maintaining an enclosed conical body of such suspension having an apex outlet and a 'base outlet passageway, force-feeding such suspension to the body tangentially thereof, discharging one fraction of suspended solids from the body through its apex outlet and another` fraction through its base outlet passageway, maintaining a substantially constant suction on the -discharge from the passageway thus establishing within thatpassageway a reduced pressure that `fluctuates with variations in the composition of the suspension fed into the body, and automatically employing such fluctuating pressures for correspondingly varying the size of the apex out- Ilet whereby to maintain substantially uniform tthe consistency of the apex discharge.

9. Apparatus for automatically controlling the consistency of the apex discharge of a hydraulic cyclone which comprises, in combination, a cyclone having a tangential feed inlet port located near the base thereof, a conduit extending from ;said base, means for producing a partial vacuum :in said conduit, an apex discharge orice, means :for varying the rate of flow of a slurry through said apex orifice, and means for actuating said iiiow varying means, said actuating means being (controlled by changes in said partial vacuum, said :How varying means being adapted to increase the iiow of slurry through said orice when said partial vacuum increases and to decrease said rate of iiow when said partial vacuum decreases.

10. Apparatus according to claim 9 wherein the means for varying the rate of ow of slurry through the apex orifice is means for varying the area of said apex orifice.

11. Apparatus according to claim 10 wherein the means for varying the rate of flo-W of slurry is a sphincter valve.

12. Apparatus according to claim 9 wherein the vacuum producing means comprises a downwardly-extending suction leg connected to the discharge end of the conduit.

13. Apparatus for automatically controlling the consistency of the apex discharge of a hydraulic cyclone which comprises, in combination, a cyclone having a tangential feed inlet port located near the base thereof, a conduit extending from said base along the central axis of said cyclone providing a discharge passageway terminating within said cyclone, a vacuum probe, the pressure sensitive portion of said probe being located Within the said conduit on the axis of said cyclone, vacuum producing means adapted to produce a partial vacuum in said conduit, an apex discharge orifice, and means for varying the rate of flow of slurry through said apex orice, said probe actuating said last-named means, whereby said rate of flow is increased when said probe responds to an increase of vacuum in said conduit and whereby said rate of ow is decreased when said probe responds to a decrease of vacuum in said conduit.

14. Apparatus according to claim 13 wherein said means for varying the rate of ow of slurry is an apex orice of variable area.

15. Apparatus according to claim 14 wherein the means for varying the rate of flow of slurry is a sphincter valve.

16. Apparatus according to claim 13 wherein the means adapted to produce a partial vacuum is a downwardly extending suction leg connected to the discharge end of the conduit.

17. As a new and useful article of manufacture, a cyclone comprising a tangential feed inlet port, a base discharge conduit, and a vacuum probe, said port being located at the base of said cyclone, said conduit extending through said base and said probe having its pressure sensitive portion located within said conduit on the central axis thereof.

ORRIN HUGHITT WRIGHT. JOSEPH LEONARD WEAVER. ELLIOT BRYANT FITCH.

References Cited in the le of this patent UNITED STATES PATENTS Name Date Samson June 5, 1945 OTHER REFERENCES Number 

